Conventionally, single screw compressors have been used as compressors for compressing refrigerant or air. For example, Patent Document 1 discloses a single screw compressor including a single screw rotor and two gate rotors.
Such a single screw compressor will be described with reference to FIG. 13. As illustrated in FIG. 13, a screw rotor (200) is formed in an approximately cylindrical shape, and a plurality of spiral grooves (201) are formed in an outer circumference thereof. Gate rotors (210) are formed in an approximately flat plate-like shape, and are arranged on sides of the screw rotor (200). A plurality of rectangular plate-like gates (211) are radially provided in the gate rotor (210). The gate rotor (210) is installed with its rotation axis being perpendicular to a rotation axis of the screw rotor (200), and the gate (211) is to be engaged with the spiral groove (201) of the screw rotor (200).
Although not illustrated in FIG. 13, in the single screw compressor, the screw rotor (200) and the gate rotors (210) are accommodated in a casing, and the spiral groove (201) of the screw rotor (200), the gate (211) of the gate rotor (210), and an inner wall surface of the casing define a compression chamber (220). When rotatably driving the screw rotor (200) by an electric motor, etc., the gate rotors (210) rotate in response to the rotation of the screw rotor (200). Subsequently, the gate (211) of the gate rotor (210) relatively moves from a start point (a left end as viewed in FIG. 13) toward a terminal point (a right end as viewed in FIG. 13) in the spiral groove (201) with which the gate is engaged, thereby gradually reducing the volume of the completely-closed compression chamber (220). Consequently, fluid in the compression chamber (220) is compressed.